I think the best answer here is, as is so often the case, to follow the manufacturer's instructions. But common sense should give us some idea. Acetolactate is oxidized non enzymatically to diacetyl in the package. If yeast are present then they will reduce the diacetyl back to acetoin and butane diol. Thus clearly you want to put the enzyme into the beer before the yeast are removed or very shortly afterwards in order to prevent that oxidation step from taking place. IOW you want to be rid of the acetolactate by the time the yeast are gone. Once the yeast are gone even this product will not remove diacetyl. It works by preventing it from forming.